Divertor remote maintenance

Remote replacement of the ITER divertor will be required several times during the life of the machine. To facilitate its regular exchange the divertor is assembled in the vacuum vessel in 54 cassettes, each being introduced into the vessel through one of three equispaced handling ports. The remote replacement of plasma facing components in the hot-cell allows the cassette bodies to be re-used and to minimise the amount of activated waste. An R&D project was conceived during the ITER EDA to demonstrate the feasibility of divertor remote maintenance operations. Two test platforms have been set up and are being used to evaluate equipment and procedures. Following a short description of the test facilities set up at ENEA Brasimone, Italy, this paper reports the test results which confirm the overall feasibility of the proposed maintenance and refurbishment schemes. 1. Divertor Maintenance Remote replacement of the ITER divertor is estimated to be required up to eight times during the life of ITER. To facilitate its replacement, the divertor is assembled in the vacuum vessel in 54 cassettes, each being introduced into the vessel through one of three equispaced handling ports. A radial mover transports each cassette along radial rails through the handling port and into the vessel where a toroidal mover lifts and transports the cassette to its designated position. To do so the toroidal mover inserts, under the cassette, two forks which include a set of jacks to lift the cassette by a few millimetres. The jacks are driven by pressurised water whilst the toroidal mover is equipped with pinions, driven by electric motors, operating against racks on the rails to index the cassette around the vessel. The central cassette (in front of the access duct) and the second cassettes, (on either side of the central cassette) are transported radially and are positioned into the vessel by the radial mover equipped with an ad-hoc end-effector. Once at its final position, a cassette is locked to the toroidal rails such that it can sustain the off-normal electromagnetic loads and is accurately aligned in both poloidal and toroidal directions. A further requirement on the divertor is to minimise the amount of activated waste to be sent to a repository. The replacement of plasma facing components in the hot-cell, i.e. the refurbishment process, allows the cassette bodies (10 t out of a total cassette weight of 12 t) to be re-used. 2. Design Changes between the 1998 ITER Design and ITER-FEAT The divertor handling scheme has not changed but it has been modified to suit the new geometry [1]. The total number of cassettes has been reduced from 60 to 54, the cassette weight from 25 to 12 t and the available space between the cassette bottom and the vessel from 240 to 70 mm. This last change, which prevents the support of a cassette from underneath during its radial translation, has led to the adoption of a cantilever multifunctional mover (CMM) for all radial transport operations. The CMM is driven by a rack-and-pinion mechanism and it moves along 2 rails fitted inside the port. It carries a manipulator arm for all dexterous operations and a 2 DOF frontend plate (lifting & tilting) that can be fitted with a number of end-effectors. The cassette toroidal mover (CTM) concept has remained unchanged. Its detailed design is being amended to accommodate the new position of the toroidal rails. Finally, the cassette cooling pipes, originally straight, need to be bent because of space limitations in the ports. FIG.1. Radial mover concepts, evolution between the 1998 design and ITER FEAT 3. The ITER Divertor Maintenance R&D Project